1. Field of the Invention
The present invention relates to pyrromethene metal complexes for use as fluorescent dye and to light emitting devices (LEDs) using the same.
2. Description of the Related Art
Organic thin-film LEDs, from which light is emitted when electrons injected from a cathode are recombined with holes injected from an anode in an organic fluorescent material between the cathode and the anode, have recently been studied with great interest. These devices are of interest because they can be formed in a thin structure, can emit light with high luminance under a low driving voltage, and can emit multicolored light depending on the fluorescent materials used.
Many research organizations have studied these elements since C. W. Tang et al of Kodak disclosed that an organic thin-film LED emits light with high luminance (Appl. Phys. Lett. 51 (12) 21, p. 913, 1987). A typical organic thin-film LED developed by Kodak comprises a hole transporting diamine compound, 8-hydroxyquinoline aluminum serving as a emissive layer, and a Mgxe2x80x94Ag cathode, in that order, on an ITO glass substrate. This LED was able to emit green light with a luminance of 1000 cd/m2 under a driving voltage of about 10 V. Some existing organic thin-film LEDs are have undergone certain modifications. For example, an electron transporting layer may be additionally disposed in a device.
Research in green emissive materials is the most advanced for multicolored emission. Red and blue emissive materials are still required to be more durable and to have high luminance and chromatic purity, and have been studied more intensely.
Exemplary red emissive materials include perylenes such as bis(diisopropylphenyl)perylene, perynone, porphyrin, and Eu complexes (Chem. Lett., 1267(1991)).
Also, a method has been studied in which a host material is doped with a red fluorescent material to generate red emission. Exemplary host materials include quinolinol metal complexes such as tris(8-quinolinolato)aluminum, bis(10-benzoquinolinate)beryllium, diarylbutadienes, stilbenes, and benzothiazoles. These host materials are doped with 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran, metal phthalocyanine complexes such as MgPc and AlPcCl, squaliriums, and violanthrones to generate red luminescence.
Unfortunately, some of the known emissive materials including host materials and dopants have low luminance efficiency and thus have a high power consumption, and others are not durable and thus result in a short lifetime of the LED. Also, concentration quenching and exciplex and excimer formations often lower the fluorescence intensity when the materials are in a thin-film state although the materials have high fluorescence when they are in a solution. Thus, many of the materials cannot provide high luminance suitable for LEDs. It is a big problem that particularly most of the red emissive materials including host materials and dopants cannot provide both high chromatic purity and high luminance, simultaneously.
In Japanese Unexamined Patent Application Publication No. 2000-208270, a diketopyrrolo[3,4-c]pyrrole derivative and an organic fluorescent material having a peak fluorescent wavelength of 580 to 720 nm are used to generate a red emission, but cannot lead to high luminance.
Accordingly, an object of the present invention is to solve the above-described problem and to provide a new pyrromethene metal complex capable of resulting in an LED having high luminance efficiency and high chromatic purity and an LED using the same.
The present invention is directed to a pyrromethene metal complex.
The present invention is also directed to an LED material comprising the pyrromethene metal complex.
The present invention is also directed to an LED generating a emission having an emission peak wavelength in the range of 580 to 720 nm by electrical energy. The device comprises at least one of: an LED material comprising a diketopyrrolo[3,4-c]pyrrole derivative and an organic fluorescent material having a fluorescent peak wavelength of 580 to 720 nm; and an LED material comprising a pyrromethene metal complex.
According to the present invention, the pyrromethene metal complex has highly fluorescent properties and therefore can be used for LEDs. By using the pyrromethene metal complex, an LED having a high energy efficiency, a high luminance, and a high chromatic purity can be achieved.
Pyrromethene metal complexes represented by the chemical formula (1) will now be described in detail. 
R1, R2, and L are each a substituent selected from the group consisting of hydrogen, alkyl, cycloalkyl, aralkyl, alkenyl, cycloalkenyl, alkynyl, hydroxyl, mercapto, alkoxy, alkylthio, aryl ether, aryl thioether, aryl, heterocyclic, halogen, haloalkane, haloalkene, haloalkyne, cyano, aldehyde, carbonyl, carboxyl, ester, carbamoyl, amino, nitro, silyl, siloxanyl, and a fused aromatic ring and an alicyclic ring formed with adjacent substituents. R1, R2, and L may be the same as or different from one another. M represents a metal having a valence of m and is selected from the group consisting of boron, beryllium, magnesium, chromium, iron, nickel, copper, zinc, and platinum. Ar1 to Ar5 represent aryl.
In these substituents, alkyl means saturated aliphatic hydrocarbon substituents such as methyl, ethyl, propyl, and butyl. Cycloalkyl means saturated alicyclic ring substituents such as cyclopropyl, cyclohexyl, norbornyl, and adamantyl. Aralkyl means substituents formed with aromatic hydrocarbons having an aliphatic hydrocarbon therebetween, such as benzyl and phenylethyl. Alkenyl means unsaturated aliphatic hydrocarbon substituents having a double bond, such as vinyl, allyl, and butadienyl. Cycloalkenyl means unsaturated alicyclic ring substituents having a double bond, such as cyclopentenyl, cyclopentadienyl, and cyclohexene. Alkynyl means unsaturated aliphatic hydrocarbon substituents having a triple bond, such as acetylenyl. Alkoxy means substituents formed with aliphatic hydrocarbons having an ether linkage therebetween, such as methoxy. Alkylthio means substituents in which sulfur is substituted for oxygen in the ether linkage of alkoxy. Aryl ethers mean substituents formed with aromatic hydrocarbons having an ether linkage therebetween, such as phenoxy. Aryl thioethers mean substituents in which sulfur is substituted for oxygen in the ether linkage of aryl ethers. Aryl means aromatic hydrocarbon substituents, such as phenyl, naphthyl, biphenyl, phenanthryl, terphenyl, and pyrenyl. Heterocyclic means cyclic substituents having an atom other than carbon, such as furyl, thienyl, oxazolyl, pyridyl, quinolyl, and carbazolyl. Halogens mean fluorine, chlorine, bromine, and iodine. Haloalkane, haloalkene, and haloalkyne mean substituents in which halogens are substituted for part or entirety of the above-described alkyl, alkenyl, or alkynyl. Aldehyde, carbonyl, ester, carbamoyl, and amino includes substituents having an aliphatic hydrocarbon, an alicyclic ring, an aromatic hydrocarbon, a heterocycle, and the like therein. Silyl means silicon compounds such as trimethylsilyl. Each above-described substituent may have a substituent therein or not. The fused aromatic ring and the alicyclic ring may have a substituent or not.
Boron complexes represented by the following chemical formula (2) have higher fluorescence quantum yield in the metal complexes represented by the chemical formula (1). 
R3 to R6 may be the same as or different from one another, and are each a substituent selected from the group consisting of hydrogen, alkyl, cycloalkyl, aralkyl, alkenyl, cycloalkenyl, alkynyl, hydroxyl, mercapto, alkoxy, alkylthio, aryl ethers, aryl thioethers, aryl, heterocyclic, halogens, haloalkane, haloalkene, haloalkyne, cyano, aldehyde, carbonyl, carboxyl, esters, carbamoyl, amino, nitro, silyl, siloxanyl, and a fused aromatic ring and an alicyclic ring formed with adjacent substituents. Ar6 to Ar10 represent aryl groups. These substituents are the same as in the chemical formula (1).
By substituting alkyl having a carbon number of 4 or more for at least one of Ar1 to Ar4 of the formula (1) and at least one of Ar6 to Ar9, of the formula (2) the dispersibility of the material is improved and thus high luminance can be obtained. Preferably, both R5 and R6 of the formula (2) are fluorine in view of the availability and the synthesis of primary materials. Exemplary pyrromethene metal complexes are represented by the following formulas. 
The pyrromethene metal complexes of the present invention may be prepared in accordance with the following procedure.
Compounds represented by the formulas (7) and (8) are heated with phosphorus oxychloride in 1,2-dichloroethane, and are followed by reacting a compound represented by the formula (9) in the presence of triethylamine. Thus, a metal complex represented by formula (1) is obtained. Ar1 to Ar5, R1 and R2, M, L, and m are the same as in the description above. J represents a halogen. 
Thus the prepared pyrromethene metal complex of the present invention is suitable for an LED material. An LED of the present invention will now be described in detail.
An anode is formed of a transparent material to transmit light. Exemplary materials of the anode include conductive metal oxides such as tin oxide, indium oxide, and indium tin oxide (ITO); metals such as gold, silver, and chromium; conductive inorganic compounds such as copper iodide and copper sulfide; and conductive polymers such as polythiophene, polypyrrole, and polyaniline. In particular, ITO glass and Nesa glass are preferably used. The resistance of the transparent anode is not limited as long as current can be supplied to ensure that light is emitted from the device, but preferably, it is low with respect to power consumption of the device. For example, a substrate with ITO having a resistance of 300 xcexa9/xe2x96xa1 or less is used for the anode. The thickness of ITO is set according to the resistance thereof and often set in the range of 100 to 300 nm. A glass substrate is formed of soda-lime glass, alkali-free glass, or the like. The thickness of the glass substrate is 0.5 or more to ensure the mechanical strength of the device. Preferably, alkali-free glass is used because few ions are eluted therefrom. Alternatively, soda-lime glass coated with SiO2 may be used. However, the substrate is not limited to being formed of glass as long as the anode can be ensured the stable function thereof, and may be formed of a plastic. ITO may be deposited by an electron beam, sputtering, a chemical reaction method, or the like and is not limited to being formed by these methods.
A cathode is preferably formed of a material capable of efficiently injecting electrons into an organic layer. Exemplary cathode materials include platinum, gold, silver, copper, iron, tin, aluminum, indium, chromium, lithium, sodium, potassium, calcium, magnesium, cesium, and strontium. In order to increase the electron-injection efficiency to improve the performance of the device, metals having a low work function, such as lithium, sodium, potassium, calcium, cesium, and magnesium, and alloys containing these metals are advantageously used. However, generally speaking, these metals having a low work function are generally unstable in the air, so for example the method of using a highly stable electrode and doping the organic layer with a small amount of lithium, magnesium, or cesium (1 nm or less in thickness when measured by a thickness meter on vacuum deposition) can be given as a preferred example. Alternatively, inorganic salts such as lithium fluoride may be used. In order to protect the cathode, preferably, a metal such as platinum, gold, silver, copper, iron, tin, aluminum, or indium or an alloy of these metals, an inorganic substance such as silica, titania, or silicon nitride, and a polymer such as polyvinyl alcohol, polyvinyl chloride, or a hydrocarbon are further laminated. Preferably, the cathode is formed by a method in which the conductivity can be ensured, such as resistance heating, electron beam, sputtering, ion plating, or coating.
The substance which brings about light emission in the present invention may comprise: (1) a hole transporting layer and a emissive layer; (2) a hole transporting layer, a emissive layer, and an electron transporting layer; (3) a emissive layer and an electron transporting layer; (4) a hole transporting layer, a emissive layer, and a hole-blocking layer; (5) a hole transporting layer, a emissive layer, a hole-blocking layer, and an electron transporting layer; (6) a emissive layer, a hole-blocking layer, and an electron transporting layer; or (7) a monolayer containing some of the materials of the above-described layers. Hence, the LED may have a multilayer structure of (1) to (6) or a monolayer structure composed of an LED material alone or including an LED material and a material of the hole transporting layer, the hole-blocking layer, or the electron transporting layer. The substance which brings about light emission, in the present invention, means substances and layers contributing to the light emission of the device, and may emit light itself or may help to emit light.
The substances of the present invention comprise a diketopyrrolo[3,4-c]pyrrole derivative having a specific structure and an organic fluorescent material having a fluorescent peak wavelength of 580 to 720 nm. Alternatively, the substances comprise a pyrromethene metal complex. These substances may be contained in any layer of the above-described layers, and preferably, are contained in the emissive layer because both substances are fluorescent.
The hole transporting layer serves to transport holes injected from the anode. Exemplary hole transporting materials include: triphenylamines, such as N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-methylphenyl)-4,4xe2x80x2-dipheny-1,1xe2x80x2-diamine and N,Nxe2x80x2-bis(1-naphthyl)-N,Nxe2x80x2-diphenyl-4,4xe2x80x2-dipheny-1,1xe2x80x2-diamine; bis(N-arylcarbazole) and bis(N-alkylcarbazole) derivatives; and pyrazolines, stilbenes, distyryl derivatives, hydrazones, heterocyclic compounds, such as oxadiazoles, phthalocyanines, and porphyrins; and polymers, such as polycarbonates and styrenes having a monomer of the above-described compounds as a side chain group, polyvinyl carbazole, and polysilanes. However, the hole transporting materials are not limited to these as long as they can be formed into a thin film and does not inhibit the transporting of holes injected from the anode. The hole transporting layer may be formed of one of the above-described materials alone, or may be formed of a plurality of materials.
The emissive layer is provided with an LED material. The LED of the present invention emits light having a peak wavelength of 580 to 720 nm by electrical energy. A light having a peak wavelength less than 580 nm cannot lead to red emission with excellent chromatic purity even if the peak width thereof is small. On the other hand, a light having a peak wavelength greater than 720 nm leads to a degraded luminous efficacy and therefore, cannot provide red emission with a high luminance. The emissive material comprises at least one of the following (a) and (b).
(a) A diketopyrrolo[3,4-c]pyrrole derivative represented by formula (3) and an organic fluorescent material having a peak fluorescent wavelength of 580 to 720 nm. 
R7 and R8 are each a substituent selected from the group consisting of alkyl having carbon numbers of 1 to 25 and substituents represented by formula (4), and may be the same or different. 
R9 and R10 are each a substituent selected from the group consisting of hydrogen, alkyl having carbon numbers of 1 to 4, phenyl having no substituent or having alkyl having a carbon number of 1 to 3 therein, and R9 and R10 may be the same or different. Ar13 is a substituent selected from the group consisting of phenyl and naphthyl having alkyl or alkoxy or halogen or phenyl, and naphthyl. n represents a whole number of 0 to 4. Ar11 and Ar12 a substituent selected from the group consisting of phenyl, naphthyl, styryl, and carbazolyl.
(b) A pyrromethene metal complex represented by the above-described formula (1).
In the case of (a), a diketopyrrolo[3,4-c]pyrrole derivative represented by formula (3) and an organic fluorescent material having a peak fluorescent wavelength of 580 to 720 nm are used as both a dopant and a host. Preferably, the diketopyrrolo[3,4-c]pyrrole derivative is used as a host and the organic fluorescent material is used as a dopant.
The compounds represented by formulas (3) and (4) will now be described in detail. Substituents R7 and R8, which are alkyl having a carbon number of 1 to 25, may have a straight chain or a side chain. Specifically, R7 and R8 may be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 1,1,3,3-tetramethylbutyl, 2-ethylhexyl, n-nonyl, decyl, undecyl, dodecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, eicosyl, heneicosyl, docosyl, tetracosyl, and pentacosyl. Preferably, R7 and R8 are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 1,1,3,3-tetramethylbutyl, and 2-ethylhexyl, which have carbon numbers of 1 to 8. More preferably, R7 and R8 are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl, which have carbon numbers of 1 to 4.
The alkyl groups having carbon numbers of 1 to 4 represented by R9 and R10 include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl. The phenyl groups represented by R9 and R10 may have alkyl with a carbon number of 1 to 3, and this alkyl includes methyl, ethyl, n-propyl, and isopropyl. The phenyl groups represented by Ar13 have at least one of alkyl, alkoxy, halogen, and phenyl and may have these substituents at up to three bonding sites, whether the substituents are the same as or different from one another. In this instance, preferably, alkyl has a carbon number of 1 to 8. Specifically this alkyl includes methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 1,1,3,3-tetramethylbutyl, and 2-ethylhexyl. The alkoxy, preferably, has a carbon number of 1 to 8, and specifically may be methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, isobutoxy, tert-butoxy, n-pentoxy, 2-pentoxy, 3-pentoxy, 2,2-dimethylpropoxy, n-hexoxy, n-heptoxy, n-octoxy, 1,1,3,3-tetramethylbutoxy, and 2-ethylhexoxy. Halogen mean fluorine, chlorine, bromine, and iodine. The phenyl which the phenyl groups represented by Ar13 have therein further has alkyl or alkoxy having a carbon number of 1 to 8. These alkyl and alkoxy are the same as in the above. Naphthyl groups represented by Ar13 include 1-napohthyl and 2-naphtyl, and may have any substituent and preferably the same substituents as in the above-described phenyl groups.
Ar11 and Ar12 are substituents selected from the group consisting of phenyl, naphthyl, styryl, and carbazolyl. The naphthyl, styryl and carbazolyl groups may be combined with diketopyrrolo[3,4-c]pyrrole skeleton at any bonding site thereof. These phenyl, naphthyl, styryl, and carbazolyl groups may have a substituent selected from the group consisting of hydrogen, cyano, halogen, alkyl, cycloalkyl, aralkyl, alkoxy, alkylthio, aryloxy, aryl thioether, aryl, heterocyclic, amino, silyl, and a fused aromatic ring and an alicyclic ring formed with adjacent substituents. Halogen is the same as in the above description. The alkyl groups may have a straight chain or a side chain and preferably have a carbon number of 1 to 25, more preferably of 1 to 8. Exemplary alkyl groups are the same as in the above description. The cycloalkyl groups, preferably, have a carbon number in the range of 5 to 12, and specifically include cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl, and cyclododecyl. More preferably, the cycloalkyl include cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl. The aralkyl groups are not limited in these carbon numbers, but preferably they have a carbon number of 7 to 24. Specifically, they include benzyl, 2-benzyl-2-propyl, xcex2-phenyl-ethyl, xcex1,xcex1-dimethylbenzyl, xcfx89-phenyl-butyl, xcfx89,xcfx89-dimetyl-xcfx89-phenyl-butyl, xcfx89-phenyl-dodecyl, xcfx89-phenyl-octadecyl, xcfx89-phenyl-eicosyl, xcfx89-phenyl-docosyl groups. Preferably, they are benzyl, 2-benzyl-propyl, xcex2-phenyl-ethyl, xcex1,xcex1-dimethylbenzyl, xcfx89-phenyl-butyl, xcfx89,xcfx89-dimetyl-xcfx89-phenyl-butyl, xcfx89-phenyl-dodecyl, and xcfx89-phenyl-octadecyl groups, and more specifically are benzyl, 2-benzyl-propyl, xcex2-phenyl-ethyl, xcex1,xcex1-dimethylbenzyl, xcfx89-phenyl-butyl, and xcfx89,xcfx89-dimetyl-xcfx89-phenyl-butyl groups. Alkylthio groups are substituents in which oxygen in the ether linkage of an alkoxy group is replaced with sulfur. An aryloxy group generally means a substituent formed with aromatic hydrocarbons having an ether linkage therebetween. In addition, in the present invention, aryloxy groups include substituents formed with an aromatic hydrocarbon having a carbon number of 6 to 24 and a saturated or unsaturated heterocycle which have an ether linkage therebetween. This hydrocarbon and heterocycle may have no substituent or have alkyl or alkoxy having a carbon number of 1 to 8 therein. The aryl thioether groups are substituents in which oxygen in the ether linkage of an aryloxy group is replaced with sulfur. The aryl groups, preferably, have a carbon number of 6 to 24, and specifically include phenyl, 1-naphthyl, 2-naphthyl, 4-biphenyl, phenanthryl, 2-fluorenyl, 9-fluorenyl, 2-anthracenyl, and 9-anthracenyl. More preferably, the aryl groups include phenyl, 1-naphthyl, 2-naphthyl, and 4-biphenyl. These aryl groups may further have alkyl or alkoxy having a carbon number of 1 to 8 therein. The heterocyclic groups have a cyclic structure having an atom other than carbon, such as nitrogen, oxygen, or sulfur. They may be saturated or unsaturated and preferably unsaturated. Specifically, they include thienyl, benzo[b]thienyl, dibenzo[b,d]thienyl, thianthrenyl, furyl, furfuryl, 2H-pyranyl, benzofuranyl, isobenzofuranyl, dibenzofuranyl, phenoxythienyl, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, bipyridyl, triazinyl, pyrimidinyl, pyrazinyl, pyridazinyl, indolizinyl, isoindolyl, indolyl, indazolyl, purinyl, quinolizinyl, quinolyl, isoquinolyl, phthalazinyl, naphthyridinyl, quinoxalinyl, quinazolinyl, quinolinyl, phthalizinyl, carbazolyl, carbolinyl, benzotriazolyl, benzoxazolyl, phenanthridinyl, acridinyl, perimidinyl, phenanthrolinyl, phenazinyl, isothiazolyl, phenothiazinyl, isoxazolyl, furazanyl, and phenoxazinyl. These heterocycle groups may further have alkyl or alkoxy having a carbon number of 1 to 8 therein. In the amino groups, at least one hydrogen of two hydrogens thereof may be replaced with alkyl having a carbon number of 1 to 25, cycloalkyl having a carbon number of 5 to 12, aryloxy including aromatic hydrocarbons having a carbon number of 6 to 24, aryl having a carbon number of 6 to 24, heterocyclic, or the like. In this instance, aryl having a carbon number of 6 to 24 and heterocyclic may further have alkyl or alkoxy having a carbon number of 1 to 8 therein. In the silyl groups, at least one of hydrogen of three hydrogens thereof may be replaced with alkyl having a carbon number of 1 to 25, cycloalkyl having a carbon number of 5 to 12, aryloxy including aromatic hydrocarbons having a carbon number of 6 to 24, aryl having a carbon number of 6 to 24, a heterocyclic group, or the like. The aryl having a carbon number of 6 to 24 and the heterocyclic may further have alkyl or alkoxy having a carbon number of 1 to 8 therein. The fused aromatic ring and alicyclic ring formed with adjacent substituents may have a substituent or not.
Preferred diketopyrrolo[3,4-c]pyrrole derivatives include the following. 
The diketopyrrolo[3,4-c]pyrrole derivatives are prepared in accordance with, for example, embodiments of EP Unexamined Patent Application Publication Nos. 0094911 and 0133156. Aromatic nitrile and diisopropyl succinate are heated together in t-amyl alcohol in the presence of potassium-t-butoxide to prepare a diketopyrrolopyrrole precursor. The diketopyrrolopyrrole precursor is heated with an alkyl halide in dimethylformamide (DMF) in the presence of potassium-t-butoxide and is followed by a general processing, Thus, the diketopyrrolo[3,4-c]pyrrole is obtained.
The diketopyrrolo[3,4-c]pyrrole derivatives of the present invention are fluorescent, and most of the derivatives have a fluorescence quantum efficiency of 0.3 or more in toluene or DMF or have a molar absorptivity of 5000 or more.
In the present invention, organic fluorescent materials having a peak wavelength of 580 to 720 nm are used to generate red emission. Specifically, the organic fluorescent materials include fused derivatives of aromatic hydrocarbons such as terylene; fused heterocyclics such as pyridinothiadiazole, pyrazolopyridine, and diketopyrrolopyrrole; naphthalimido derivatives such as bis(diisopropylphenyl)perylenetetracarboxylic imido; perynones; rare earth complexes such as Eu complexes of which the ligand is acetylacetone or benzoylacetone and phenanthroline; 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran and the analogues thereof; metal phthalocyanine derivatives such as magnesium phthalocyanine and aluminum chlorophthalocyanine; metalloporphyrin derivatives such as zinc porphyrin; thiophenes; pyrroles; rhodamines; deazaflavin derivatives; coumarin derivatives; oxazines; phenoxazines; phenoxazones; quinacridones; benzothioxanthene and the analogues thereof; and dicyanoethenylarenes.
Preferably, the organic fluorescent materials have a pyrromethene skeleton represented by formula (5) or a metal complex thereof to generate a red emission having excellent chromatic purity. 
At least one of R11 to R17 has an aromatic ring or form a fused ring with an adjacent substituent. The others are each a substituent selected from the group consisting of hydrogen, alkyl, cycloalkyl, aralkyl, alkenyl, cycloalkenyl, alkynyl, hydroxyl, mercapto, alkoxy, alkylthio, aryl ethers, aryl thioethers, aryl, heterocyclic, halogens, haloalkane, haloalkene, haloalkyne, cyano, aldehyde, carbonyl, carboxyl, esters, carbamoyl, amino, nitro, silyl, siloxanyl, and a fused aromatic ring and an alicyclic ring formed with adjacent substituents. X represents carbon or nitrogen. If X is nitrogen, R17 does not exist. The metal of the metal complex is selected from the group consisting of boron, beryllium, magnesium, chromium, iron, nickel, copper, zinc, and platinum.
These substituents are the same as in formula (1). Preferably, the organic fluorescent materials have a high fluorescence quantum yield to ensure increased luminance. Preferably, the following complex represented by formula (6) is used as a metal complex of the organic fluorescent materials having the pyrromethene skeleton. 
At least one of R18 to R24 has an aromatic ring or form a fused ring with an adjacent substituent. The others are each a substituent selected from the group consisting of hydrogen, alkyl, cycloalkyl, aralkyl, alkenyl, cycloalkenyl, alkynyl, hydroxyl, mercapto, alkoxy, alkylthio, aryl ethers, aryl thioethers, aryl, heterocyclic, halogens, haloalkane, haloalkene, haloalkyne, cyano, aldehyde, carbonyl, carboxyl, esters, carbamoyl, amino, nitro, silyl, siloxanyl, and a fused aromatic ring and an alicyclic ring formed with adjacent substituents. X represents carbon or nitrogen. If X is nitrogen, R24 does not exist.
These substituents are the same as in formula (1).
More preferably, the pyrromethene metal complex represented by formula (1) is used to prevent the degradation of fluorescence intensity in a thin-film state and thus to generate light with high luminance.
Besides the metal complex represented by formula (1), exemplary metal complexes of the organic fluorescent materials having the pyrromethene skeleton include the following. 
In order to transfer energy from a host material to dopant, it is important that the fluorescence spectrum of the host material overlaps the absorption spectrum (excitation spectrum) of the dopant. The fluorescent spectrum of a host, here, is measured when the host is in a thin-film state and the absorption (excitation) spectrum and the fluorescent spectrum of dopant are measured when the dopant is in a solution state. This is because the host is in a thin-film state and the dopant molecularly doped in the host is in almost the same state as in a solution, in the LED. If a material having excellent chromatic purity, such as the above-described substances having a pyrromethene skeleton and metal complexes thereof, is used as a dopant, the dopant exhibits a small Stokes shift (the difference between the peaks of the excitation spectrum and the fluorescent spectrum) of several to tens of nanometers. When the dopant is used for generating a red emission having a peak wavelength of 580 to 720 nm and high chromatic purity, the dopant exhibits an absorption (excitation) spectrum in the areas of yellow, golden yellow, orange, tango, and red (in the range of 540 to 720 nm). If a host material exhibits a fluorescent spectrum in a shorter wavelength band of yellowish green, green, blue green, blue, lavender, and purple than the yellow band and thus the overlapped spectrums is small, energy transfer becomes difficult and thus light may not be emitted from the dopant. If emitted, the light would be whitened due to partial emission from the host material and thus would not become red with high chromatic purity.
Accordingly, the host material preferably has a fluorescent peak wavelength of 540 to 720 nm, so that the dopant can emit light of 580 to 720 nm with high luminance and high chromatic purity. Substances having a yellow, golden yellow, an orange, a tango, and a red fluorescence correspond to such host materials. When a diketopyrrolo[3,4-c]pyrrole derivative represented by formula (1) is used as a host material, therefore, the derivative preferably has a yellow, a golden yellow, an orange, a tango, or a red fluorescence.
In the case of (b), the LED material comprises a diketopyrrolo[3,4-c]pyrrole derivative represented by formula (1).
It has been known that pyrromethene metal complexes are particularly used for dopant to generate light with high luminance and that red emission is generated by introducing aromatic rings to the 1-, 3-, 5-, and 7-positions of the pyrromethene skeleton of the complex. However, the known pyrromethene compounds are liable to cause concentration quenching, and therefore cannot lead to sufficient red emission. Introducing a substituent to the 8-position of the pyrromethene skeleton decreases the concentration quenching because of the advantageous stereostructual and electronical effects of the substituent. On the other hand, if the substituent at the 8-position can rotate, the fluorescence quantum yield of the pyrromethene metal complex is degraded. In the present invention, by introducing an aryl group to the 8-position of the pyrromethene skeleton to prevent the rotation thereof, a high fluorescence quantum yield and degraded concentration quenching can be achieved. This prevention of the rotation is ensured by Ar1 and Ar4 of formula (1) and Ar6 and Ar9 of formula (2), which are aryl groups. The pyrromethene metal complexes of the present invention may be used as a host, but preferably, they are used as a dopant because they have a high fluorescence quantum yield and a small half band width of the emission spectrum.
Since excessive doping causes concentration quenching, 10 weight percent of dopant is, preferably, used for the host material. More preferably, 2 weight percent of the dopant is used for the host material. The dopant may be provided by codeposition with the host material. Alternatively, the dopant and the host material are mixed with each other and then are simultaneously deposited. The dopant may be contained in part of the host material or the entirety of the host material. The dopant may be laminated as a layer or be dispersed in the host material. Since even an extremely small amount of a pyrromethene metal complex can emit light, the pyrromethene metal complex may be disposed between host layers. The dopant applied to the LED material is not limited to only one of the above-described pyrromethene metal complexes, and a plurality of pyrromethene metal complexes may be mixed. Alternatively, a pyrromethene metal complex may be mixed with at a known dopant. Exemplary known dopants which can be mixed include naphthalimido derivatives such as bis(diisopropylphenyl)perylenetetracarboxylic imido; perynone derivatives; rare earth complexes such as Eu complexes of which the ligand is acetylacetone or benzoylacetone and phenanthroline; 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran and the analogues thereof; metal phthalocyanine derivatives such as magnesium phthalocyanine and aluminum chlorophthalocyanine; rhodamines; deazaflavin derivatives; coumarin derivatives; quinacridone derivatives; phenoxazines; and oxazines.
Exemplary host materials include the diketopyrrolo[3,4-c]pyrrole derivatives having the specific substituents; other pyrrolopyrrole derivatives; fused aromatic ring compounds such as anthracene and pyrene; metal-chelated oxynoid compounds such as tris(8-quinolinolato)aluminum; bisstyryl derivatives such as bisstyrylanthracene derivatives and distyrylbenzene derivatives; tetraphenylbutadienes; coumarin derivatives; oxadiazoles; pyrrolopyridines; perynone derivatives; cyclopentadienes; thiadiazolopyridines; and polymers such as polyphenylene vinylenes, polyparaphenylenes, and polythiophenes.
An electron transporting material needs to efficiently transport electrons injected from the cathode between the electrodes where an electric field is applied. Preferably, the electron transporting material has a high electron injection efficiency and efficiently transports the injected electrons. Hence, the electron transporting material, preferably, has a high electron affinity and electron mobility with thermal and electrochemical stability. Preferably, the electron transporting material produces few impurities when it is prepared and used. Exemplary electron transporting materials include quinolinol metal complexes such as 8-hydroxyquinoline aluminum, tropolone metal complexes, flavonol metal complexes, perylenes, perynones, naphthalenes, coumarin derivatives, oxadiazoles, aldazines, bisstyryl derivatives, pyrazines, oligopyridines such as bipyridine and terpyridine, phenanthrolines, quinolines, and aromatic phosphorus oxides. These materials may be used independently or be mixed or deposited with other electron transporting materials.
In order to more efficiently generate pure red emission, the recombination of holes with electrons must occur with high probability in the emissive layer, but not in the other layers. When a diketopyrrolo[3,4-c]pyrrole derivative is used for a emissive material, preferably, the ionization potential of the electron transporting material is 5.9 eV or more. The electron transporting material needs to be stable against power distribution for long hours in order to maintain a stable red emission over time. On this account, the electron transporting material, preferably, has a molecular weight of 400 or more, more preferably of 500 or more, and further more preferably of 600 or more. This is because many of the materials having a molecular weight less than 400 are easily affected by heat. In order to form a heat-resistant electron transporting layer, it is important to consider the glass-transition temperature of materials. A material having a higher glass-transition temperature results in a more stable amorphous layer. Preferably, the electron transporting material has a glass-transition temperature of 90xc2x0 C. or more, more preferably of 110xc2x0 C., and further more preferably of 150xc2x0 C. As such an electron transporting material, organic compounds having a structure in which a plurality of skeletons are combined with each other having a conjugated bond, an aromatic hydrocarbon group, an aromatic heterocyclic group, or a combination of these groups therebetween are preferably used. The skeletons of the above-described derivatives can be directly used as the skeleton of the electron transporting material. Preferably, the skeleton has at least one quinoline ring or phosphorus oxide.
The hole-blocking layer prevents holes from moving without the recombination of holes injected from the anode with electrons injected from the cathode between the electrodes where an electric field is applied. The hole-blocking layer increases the provability of the recombination, depending on materials of layers, and thus improves the luminance efficiency of the LED. For the material of the hole-blocking layer, therefore, a substance is selected which has a lower energy level of the highest occupied molecular orbital than that of the hole transporting material and which rarely produce an exciplex with an adjacent layer. Since materials capable of transporting electrons can efficiently block holes, the above-described electron transporting materials are preferably used as a material of the hole-blocking layer.
The hole transporting layer, the emissive layer, the electron transporting layer, and the hole-blocking layer are formed by depositing the respective materials independently or by mixing at least two materials. Alternatively, the materials may be dispersed in a binding polymer including solvent soluble resins such as polyvinyl chloride, polycarbonate, polystyrene, poly(N-vinylcarbazole), polymethylmethacrylate, polybutylmethacrylate, polyester, polysulfone, polyphenylene oxide, polybutadiene, hydrocarbon resin, ketone resin, phenoxy resin, polysulfone, polyamide, ethyl cellulose, vinyl acetate, ABS resin, and polyurethane and hardening resins such as phenol resin, xylene resin, petroleum resin, urea resin, melamine, unsaturated polyester, alkyd resin, epoxide resin, and silicone resin.
The substances in the present invention is formed by resistance heating evaporation, electron beam evaporation, sputtering, molecular deposition, coating, or the like, and the method is not limited to these. Generally, resistance heating evaporation and electron beam evaporation are preferable in view of the performance of the LED. The thickness of the substance is set between 1 to 1000 nm depending on the resistance thereof.
Mainly direct current is used as electrical energy, and pulse current or alternating current may be used. It is preferable to set a current value and voltage as low as possible with respect to power consumption and the lifetime of the device.
The LED of the present invention may be used for matrix-type displays and segment-type displays. In a matrix system, pixels of a display are arrayed in a matrix, and images including characters are displayed by aggregating the pixels. Size and shapes of the pixels depend on use. For example, square pixels having a side length of 300 xcexcm or less are used for displaying images and characters on personal computers, monitors, and TVs. Pixels having a side length of the order of millimeters are used for large-screen displays such as instruction panels. In the case of monochrome displays, single color pixels are arrayed. In the case of color displays, red, green, and blue pixels are arrayed in typically a stripe arrangement or a delta arrangement. Matrix-type displays may be driven by a line-sequential system or an active matrix system. While the line-sequential system has a simple structure, the active matrix system can have an advantage in driving performance. These driving systems are selected according to use.
In the segment system, a pixel pattern is formed so that predetermined information is displayed and thus light is emitted at predetermined areas. Exemplary segment-type displays include hour plates of digital clocks, temperature indicators, operation indicators of audiovisual apparatuses and electromagnetic cooking devices, and indicator panels of automobiles. The matrix system and the segment system may coexist in a display panel.